In general, vertical cavity surface emitting lasers (VCSELs) must incorporate both a means for confining the injection current and a means for forming an optical waveguide. VCSELs may be configured to emit either through the substrate (bottom-emitting) or through the top of the structure (top-emitting), and each configuration has been characterized by a particular device structure. The bottom-emitting devices have generally employed mesas etched through the top mirror stack, and perhaps through the gain regions as well. With the addition of a contact metal on the top of the mesa, optical waveguiding and current confinement are achieved. However, for many reasons such as packaging and reliability, a mesa etched structure is undesirable. Also, the mesa structure produces a very strong optical waveguide which tends to operate in many lateral modes, leading to an unstable output beam and poor coupling to optical systems or fibers. Top emitting VCSELs have generally employed gain-guided structures where the current is confined by ion implanting a resistive region into the top layers, and where the combination of the injected current and the temperature distribution across the device serves to provide the optical waveguide. These devices have increased thresholds and instabilities under modulation. There is thus a pressing need for a top emitting device with good current confinement and a stable optical waveguide.
It is the purpose of this invention to provide a new and improved method for fabricating a VCSEL with a built-in optical waveguide accurately aligned to the current distribution.
It is a further purpose of this invention to achieve the stable optical waveguide in a nearly planar device structure.
It is a further purpose of the invention to achieve this alignment of the optical waveguide and injected current using simple fabrication means.